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Questions tagged [fft]

FFT is an acronym for Fast Fourier Transform. Use this tag for FFT-related questions. Try to also select a specific chip or software tag when possible.

2
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2answers
109 views

How to find the source of a noise in a particular band

The problem: The ADSL2+ service at home is not performing up to its potential. The modem is supposed to sync at 16 Mbps (downstream) but the it does only up to 11.5 Mbps. Using the diagnostic tools ...
0
votes
0answers
21 views

Transfer Function Estimate and PSD

I am looking at using Matlab to estimate the transfer function of an unknown system using input and output time history data. I found this page: https://www.mathworks.com/help/dsp/ug/estimate-the-...
1
vote
2answers
54 views

Frequency Response Function Estimate via FFT Question

I want to estimate the FRF of a dynamic LTI system given experimental input and output data. I know generally the approach is to use a chirp as an input to make sure enough frequency content is ...
-2
votes
2answers
70 views

dsPIC33E ADC to FFT help

I am sampling an audio range signal with a bandwidth of 3100Hz and then applying a FFT using the DSP library example from Microchip to determine the most dominant frequency of the signal. On the last ...
1
vote
0answers
179 views

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV?

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV? Cause of reason: The reason for this is that I've a modeled a LISN in LTspice where I want to simulate ...
0
votes
1answer
94 views

Can the transient response of a system be calculated using FFT and inverse FFT?

I have a system, its input and output has the following relationship. I want to know the transient response of the system with respect to a ramping input Xi=t, by solving the differential equation, ...
0
votes
0answers
47 views

What could be the source of this noise?

Below is the output of an accelerometer when it is standing still: The zoomed 0.5 seconds of time series voltage data above is from a 4 seconds of measurement with a data acquisition board at 30kHz ...
0
votes
3answers
81 views

Why is the dB of the FFT plots exceeding 96dB for these signals sampled by an 16 bit ADC

There is a 16-bit data acquisition board and below is the recording of 120 seconds of voltage input at 500Hz sampling rate. The blue plot corresponds to the input voltage Vin and the green plot output ...
-1
votes
1answer
63 views

How to change FFT spike to curve

The first picture is a part of my circuit and the voltage pass through the high filter circuit. The second picture shows an FFT spike which is obtained from the .csv file created by oscilloscope. I ...
0
votes
0answers
27 views

non-negative FFT spectrum, subtlety

definations \$x(t)\$ is a function of time. Physically, it can be voltage, displacement, magnetization and so on. It can be real, complex, vectors or more fancy numbers. \$C(t)\$ is the auto ...
0
votes
0answers
383 views

Interpretation of FFT FMCW Doppler radar results

After a lot of research and help from the users here, I managed to do some FFT and signal processing in my first time in my life :) I have got the following figure, which shows one peak frequency, ...
0
votes
0answers
107 views

Getting the velocity in Radar FMCW

I have managed to get the frequency (the beat) frequency from an FMCW. Here is a screen shot of a wall that's detected by the Radar. I performed an FFT of complex I,Q data. My questions are 1. How ...
0
votes
1answer
527 views

Applying FFT on I/Q signal to get range and velocity

I managed to get correct I/Q signal from an FMCW radar. From my last questions I understand that I have to do FFT on the root of I^2+Q^2 so I will have an array of I^2+Q^2 then do FFT on it. My ...
0
votes
1answer
123 views

Signal processing of an IVQ-3005 Radar Module

I'm going to use that module for detecting range, velocity and angle, for that radar. https://www.innosent.de/fileadmin/media/dokumente/datasheets/180222_Datenblatt_IVQ-3005.pdf So I have read a lot ...
0
votes
2answers
86 views

A sensor which can measure the vibration of a material

I am planning on making a musical instrument where I require the conversion of vibration of a material to voltage. The idea is to make a percussion instrument where I hit a plate made of a certain ...
3
votes
3answers
128 views

Help interpreting strange spectrum

I am sampling a sinusoidal signal with an oscilloscope and viewing its spectrum using the FFT mode. The signal in time domain is this: and I am getting this spectrum: The peak above the red line is ...
1
vote
0answers
331 views

Wrong FFT result when using rfft function on STM32F4

I'm trying to use rfft function in STM32F407G and I am getting wrong results when I compare it with an online fft calculator . I give a sample input as {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,...
8
votes
3answers
1k views

What's the junk at the end of my FFT in LTSPICE?

Why do FFTs have junk on the high frequency end? Suppose I go to simulate this circuit in LTSPICE: simulate this circuit – Schematic created using CircuitLab Where the LTSPICE sine and ...
3
votes
1answer
362 views

Getting different FFT results in LTspice comparing to MATLAB and Python

I have a 10 seconds of sampled data. Sampling rate is 1kHz. I uploaded the text file which is a two column time vs voltage data; it can be downloaded here. I performed FFT in MATLAB, Python and ...
0
votes
2answers
1k views

How to choose a cut-off frequency by interpreting FFT

I have a question concerning low pass filtering of IMU acceleration and gyro data. To choose a reasonable cut-off frequency, I thought about making some observations in the spectrum. Now I have some ...
7
votes
6answers
3k views

Audio spectrum analysis: PC Software vs Hardware Spectrum Analyzer

I need to do some audio spectrum analysis (basically, listening to a machine and tell if it is properly calibrated). I will record the sound it makes with a microphone (it sounds differently if it is ...
0
votes
1answer
73 views

AM radio Attenuation.

I have built the following AM radio circuit : I was able to pick several radio stations. I fixed the variable capacitor so that I can only hear the 1230 kHz station which I identified from the FCC ...
0
votes
1answer
30 views

A signal noise analysis method question for a transducer

Let's say a transducer's desired signal is p(t), and the transducer's frequency of interest is 100Hz. And let's assume we dont know the total signal x(t) which is the desired signal plus the noise and ...
0
votes
1answer
42 views

Why averaging in Spectral magnitude domain not in complex domain to estimate spectrum of a process

Consider we need the magnitude spectrum of the signal. Signal is recorded in \$N\$ trials to a certain stimuli. Signal varies from each trial because of noise. So, to estimate the actual magnitude ...
0
votes
1answer
77 views

How to scale output of butterfly unit radix 2 for further stages?

I am designing 8 point FFT by radix 2 using verilog. I am using radix 2 butterfly unit with 8 bits input and so output. I expect to be 8 bit so that I can use this structure again and again for ...
1
vote
1answer
62 views

FPGA Frequency Domain Based Beidou-3 B2a Coarse Acquisition Processor Using FFT

I'm using an ARM+FPGA platform to capture B2a (BeiDou or COMPASS) signals and determine the user position, velocity and precise time (PVT). The C/A frequency of B2a is 10.23MHz. If my sample rate is ...
1
vote
1answer
104 views

fast Fourier Transform difference with discrete Fourier Transform

I'm a french student in engineering and I'm given a kind of mandatory technical project to work out on until February. I must investigate the following article: Precise and fast spatial-frequency ...
17
votes
6answers
6k views

Why use the fast Fourier transform for noise reduction instead of a classical electronic filter?

I'd like to know how to remove environmental noise from a speech recording. I've made some research and I've noticed that most of the methods proposed use the fast Fourier transform. But why can't ...
1
vote
0answers
483 views

RFFT on 8192 samples in Q15 with CMSIS

I need to perform an FFT on a block of 8192 samples on an STM32F446 microcontroller. For that I wanted to use the CMSIS DSP library as it's available easily and optimised for the STM32F4. My 8192 ...
0
votes
1answer
42 views

Linear Frequency Dependent IQ Distortion

I want to design FD (frequency dependent ) IQ (In-phase,Quadrature) distortion that changes the phase mismatch linearly like a+b*K ( where K is 1 to 64) and amplitude remains constant to test my ...
1
vote
2answers
329 views

Gain factor in real Resistance and Reactance (AD5933)

I'm trying to develop a system for bioimpedance measurement with the IC AD5933. The AD5933 is a high precision impedance converter system that combines a frequency generator with a 12-bit, 1 MSPS, ...
1
vote
1answer
203 views

Why do I get a high peak in my FFT plot of a 50 Hz sine wave?

I am plotting the FFT of my signal that is stored in "Array" format obtained from simulation. The signal is a sine wave of 50 Hz so I get a peak at 50 Hz. The problem is that the value is way too high....
0
votes
2answers
304 views

AXI interface of an FFT core expecting more data than it should

I am working with the FFT v9.0 core from Xilinx. The FFT is configured to use the Radix-4 Burst I/O architecture. When I reach the last element of my signal, I set ...
0
votes
2answers
129 views

A question about interpreting and reducing high frequency noise in a low level square wave

As a part of a circuit the output section of the circuit is as follows(C1 is actually 10u): The input is a 1kHz 0V…5V pulse train coming from the output of a 74HC74, and the output is a square wave ...
0
votes
1answer
73 views

Suppress Certain Overtones In A Musical Instrument's Sound Wave

So, just like the title suggests, my college professor and I are trying to suppress certain overtones of an instrument's sound. I have a microphone hooked up to an oscilloscope, and I'm using the ...
1
vote
2answers
3k views

What do we mean by “ FFT points ”?

Can someone please tell me about FFT Points? I know that The Discrete Fourier Transform (DFT) is a mathematical operation, and that The Fast Fourier Transform (FFT) is an efficient algorithm for the ...
2
votes
3answers
206 views

Raise SNR of pulse signal by passive LC filter

I have a weak pulse signal, rise time 1us, fall time 10us, 0.01 to 200 pulses per second, dead time between pulses is random, along with mostly ‘white’ noise. The system has two goals of extracting ...
-2
votes
1answer
54 views

Using ieee.proposed package for a dft. Quartus showing just 10 logic elements corresponding to just 10 states. [closed]

Can anyone suggest possible reasons why this might be happening? Compilation is succesful. We have analyzed the code. Can't figure out any logical errors or syntax errors(else wouldn't compile).
0
votes
3answers
728 views

How to detect the fundamental frequency of a human singing voice signal

I want to make a digital hardware chip that can input a human voice, (singing simple wordless long notes) and output a square wave that is the same frequency as the fundamental frequency of the voice. ...
0
votes
1answer
171 views

FFT in LabView using DAQ

Familiar with the FFT and LabView. Can I use LabView to compute and display the FFT of an analog signal in real-time rather than computing it from a data array?
5
votes
3answers
862 views

Fast Fourier Transformation of incomplete signals

I would like to perform a FFT on a signal with equally sampled values of which some are missing. (Actually, they are not even missing, but simply erroneous, so I can't use them, but I can detect when ...
2
votes
2answers
5k views

Uniform Linear Array (ULA) beamwidth and angular resolution using FFT

I have a four element uniform linear array receiver and I want to know what will be the angular resolution if I perform perform Fast Fourier Transform (FFT) over antenna elements. As I think that it ...
1
vote
2answers
116 views

Number of samples (n) and number of data points (N)

I have a question: I am doing some research on the FFT and had an inquiry. If I have a fixed number of samples per period, what is the effect of increasing my data points, say from 128 to 256? I know ...
2
votes
3answers
899 views

FFT Using Pic Microcontroller [closed]

Good Evening, I am fairly unfamiliar with DSP and want to engage in a project. I wish to perform a FFT on the source current going into a non-linear load and observe its harmonic content on an LCD. ...
0
votes
2answers
223 views

FMCW Radar Working Logic Help

In fmcw radar rather than sending a signal at constant freq. we are sending a chirp which goes e.g. from 6-GHz to 6.1-GHz in 5ms. What i cannot fit in my mind is this:(Nmbers are just for example) ...
1
vote
4answers
737 views

Precision Full-Wave Rectifier: Why is the signal's biggest magnitude at DC?

I built a Precision Full Wave Rectifier Circuit, like in the following figure( with better amplifiers) to rectify a sine wave of 1kHz. As expected i got a rectified wave with 2kHz but doing its FFT ...
0
votes
3answers
273 views

Does FFT plot in an oscilloscope indicates the division or span of the frequency?

When measuring voltages V per division is indicated. If the scope shows 10mV/div it means each square's horizontal edge represents 10mV. Is that the same with FFT graph? Here is an example: The ...
1
vote
1answer
152 views

Need some advice- Should I use the CORDIC FFT function or write code for an FFT function myself? [closed]

I'm currently working on designing a filter in VHDL for a project based on an FPGA. The filter would require FFT and I've heard about the CORDIC FFT function but never used it so I'm not sure how ...
0
votes
1answer
244 views

Estimation of impedance in MATLAB

Good Morning, I'm developing a bio-impedance system. To perform the impedance calculation, I am trying to use the method described in this article, and mentioned below: http://www.ijirset.com/upload/...
2
votes
1answer
238 views

Need a device to calculate the FFT more than 100 times per second (my scope is maxed out at 10hz)

I'm writing some Python code which retrieves the FFT data that is generated in my Rigol DS1102E oscilloscope via its USB connection. My trouble is that no matter what time scale I set, I get no more ...